This invention relates to an envelope for a display device such as a liquid crystal display device, a plasma display device, a fluorescent display device or the like and a method manufacturing the same, and more particularly to an improvement in formation of spacers serving to keep an interval between an anode substrate and a flat plate constant in an envelope for a display device.
A display device such as a liquid crystal display device, a plasma display device, a fluorescent display device or the like generally includes an envelope formed of an anode substrate and a flat plate arranged opposite to each other. For this purpose, there has been conventionally known in the art a structure wherein glass beads are interposedly arranged between the anode substrate and the flat plate so as to act as spacers or studs therebetween, to thereby keep an interval therebetween constant. Such studs are formed in the envelope in such a manner as shown in FIGS. 5A to 5F.
More particularly, a substrate 1 made of glass is washed and then coated on an inner surface thereof with a transparent conductive film such as an ITO film or a thin aluminum film to form wirings and anode conductors thereon. Then, liquid for forming a photoadhesive photosensitive film 2 or a photosensitive film which exhibits adhesion when it is exposed to light such as ultraviolet rays is applied to the whole inner surface of the substrate 1 by spin coating or the like. For this purpose, a p-diazonium-N,N'-dimethyl aniline-zinc chloride double salt such as a material commercially available under a trademark "PDMA" from Tokyo Kasei Kogyo Kabushiki Kaisha may be used as liquid for the photosensitive film 2.
Then, a mask 3 which is formed so as to permit portions of the substrate 1 on which studs are to be formed to be exposed to ultraviolet rays therethrough is positioned above the substrate 1 and then ultraviolet rays are irradiated to the photosensitive film 2 through the mask 3. This permits the portions of the film 2 exposed to the rays to exhibit adhesion. Then, the exposed portions of the photosensitive film 2 each are coated with an oxide solder 4 mainly consisting of low-melting glass.
Thereafter, glass beads 5 each are placed on the oxide solder 4. Then, the substrate 1 on which the glass beads 5 are placed is heated to a temperature of 400.degree. to 600.degree. C., resulting in being calcined. The heating also causes decomposition and volatilization of the photosensitive film 2 and softening of the oxide solder 4, to thereby bond the glass beads 5 onto the substrate 5 by fusion. Finally, a casing 6 is sealed onto the substrate 1 through the glass beads 5, resulting in an envelope being formed.
However, it was found that formation of the studs by the conventional process described above exhibits some important disadvantages.
In the conventional method, it is required to deposit the oxide solder 4 on the adherent photosensitive film 2 provided on each of the positions on the substrate on which the studs are to be formed. Unfortunately, this causes adhesion properties of the photosensitive film 2 to be deteriorated to a degree sufficient to fail in satisfactory fixing of the glass beads 5 onto the substrate 1 through the film 2, leading to a failure patterning.
More particularly, although an increase in amount of the oxide solder 4 used permits the fixing of the glass beads 5 onto the substrate 1 through the solder 4, it causes temporary holding of the glass beads 4 on the substrate 1 through the adhesive photosensitive film 2 to be deteriorated, leading to displacement of the studs. On the contrary, a decrease in amount of the oxide solder 4 used ensures that the photoadhesive photosensitive film 2 exhibits adhesion sufficient to satisfactorily carry out temporary holding of the glass beads 5 onto the substrate 1, however, fixing of the glass beads 5 onto the substrate 1 is insufficient.
Also, the conventional process is so constructed that the oxide solder 4 is arranged only between the glass bead 5 and the substrate 1. Such arrangement of the oxide solder 4, when the casing 6 is sealed to the substrate 1, fails to adhere each of the glass beads 5 to a front cover or plate of the casing 6, resulting in failing to arrange the glass bead or stud 5 in the envelope with increased strength.